Reactor performance enhancement under periodic operation for the ethanol dehydration over gamma-alumina, a reaction with a stop-effect

The possibility of enhancing reactor performance under forced cycling of the inlet feed was investigated for the ethanol to ethene dehydration reaction over gamma-alumina. This reaction presents a stop-effect, i.e. a drastic increase of the reaction rate for a stepwise decrease in the inlet concentration of ethanol (Koubek et al., 1980a, b; Moravek and Kraus, 1984). This phenomenon is due to an educt inhibition, leading to the existence of an optimal inlet concentration of ethanol under steady-state conditions. Periodic operation can be used advantageously to increase the performance of the ethene production up to values higher than the maximal steady-state value. The maximum enhancement is achieved for short non-symmetric periods, with the major part of the cycle under inert gas. It was shown by simulations that for an integral reactor the parameters of the cycle have to be adjusted to the residence time. Finally the two-sites model developed for the stop-effect (Golay et al., 1997, 1999) is able to predict qualitatively the influence of all the cycle parameters

Catalyst development for the selective methylation of catechol

Gas-phase alkylation of catechol with methanol on g-alumina and modified g-alumina catalysts is studied exptl. By limiting the conversion of X < 0.3, the formation of polymethylated species can be avoided and only the three isomers guaiacol, 3-methylcatechol and 4-methylcatechol are obsd. Optimizing the catalyst compn. and the reaction conditions, a selectivity of 0.75 for the industrially most valuable product 3-methylcatechol can be obtained. [on SciFinder (R)

Role of complement and antibodies in controlling infection with pathogenic simian immunodeficiency virus (SIV) in macaques vaccinated with replication-deficient viral vectors

<p>Abstract</p> <p>Background</p> <p>We investigated the interplay between complement and antibodies upon priming with single-cycle replicating viral vectors (SCIV) encoding SIV antigens combined with Adeno5-SIV or SCIV pseudotyped with murine leukemia virus envelope boosting strategies. The vaccine was applied via spray-immunization to the tonsils of rhesus macaques and compared with systemic regimens.</p> <p>Results</p> <p>Independent of the application regimen or route, viral loads were significantly reduced after challenge with SIVmac239 (p < 0.03) compared to controls. Considerable amounts of neutralizing antibodies were induced in systemic immunized monkeys. Most of the sera harvested during peak viremia exhibited a trend with an inverse correlation between complement C3-deposition on viral particles and plasma viral load within the different vaccination groups. In contrast, the amount of the observed complement-mediated lysis did not correlate with the reduction of SIV titres.</p> <p>Conclusion</p> <p>The heterologous prime-boost strategy with replication-deficient viral vectors administered exclusively via the tonsils did not induce any neutralizing antibodies before challenge. However, after challenge, comparable SIV-specific humoral immune responses were observed in all vaccinated animals. Immunization with single cycle immunodeficiency viruses mounts humoral immune responses comparable to live-attenuated immunodeficiency virus vaccines.</p

Methylation of biphenyl over zeolite HZSM-5 in gas phase with methanol in presence of water: effect of the catalyst impregnation by tetraethyl orthosilicate

The gas phase methylation of biphenyl with MeOH over HZSM-5 and HZSM-5 modified with Si(OEt)4 was investigated at atm. pressure in the presence of water. The modification of the outer surface of the catalyst pellets by silicate gives increased selectivity to 4,4'-dimethylbiphenyl. Modified HZSM-5 gave 75% selectivity to 4-methylbiphenyl. [on SciFinder (R)

Model discrimination for reactions with stop-effect

The stop-effect, a drastic increase of the reaction rate when the feed concn. of a reactant is switched to zero, was studied for the dehydration of ethanol to ethylene on y- alumina at 180 and 200 DegC. Two basic models exist in the literature to describe this phenomenon. They were discriminated on the basis of transient and periodic expts., coupled with FTIR data of the adsorbed species. The model that best describes these measurements postulates the adsorption of ethanol on two different sites, S1 and S2, with a free S2 site being necessary for ethylene formation. [on SciFinder (R)

Oxidative coupling of toluene under periodic conditions on Pb/Li/MgO: a selective pathway to 1,2-diphenylethane

Toluene oxidn. over Pb/Li/MgO is investigated in a tubular fixed bed reactor at low conversions. A periodic process alternating toluene oxidn. in absence of oxygen in the feed and regeneration of the catalyst by oxygen presents important changes in product distribution in comparison with steady-state oxidn. Periodic conditions increase the selectivity in favor of the coupling reaction which leads to 1,2-diphenylethane and avoid formation of oxygenated products. [on SciFinder (R)